1. Field of the Invention
This invention relates to a wheel for an in-line skate, more particularly to a wheel with a hub that has wings which are capable fulcruming about a stem of the hub when an external force is applied to the wings, enlarging the incremental deformation of the tire and conserving its rebound ability under
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional in-line roller skate wheel 10 disclosed in U.S. Pat. No. 5,573,309. The wheel 10 includes a ring-shaped hub 11 defining a central bore, a pair of opposite bearings 12 mounted in the central bore, and a solid tire 13 mounted on the hub 11. The hub 11 has two opposite cylindrical tire receiving shoulders 111 and a ring-shaped tapered tire deflection controlling rim 112 that extends radially and outwardly and that is tapered from end edges of the shoulders 111. The solid tire 13 includes a rim connecting portion 131 that securely embraces the shoulders 111 and the rim 112, and a ground engaging portion 132 that reduces and that projects radially and outwardly from the rim connecting portion 131.
As illustrated in FIGS. 3 and 4, the conventional wheel 10 is disadvantageous in that the ground engaging portion 132 of the tire 13 flattens when the skater (not shown) tips slightly or sharply (see FIGS. 3 and 4) and pushes against the ground to make a turn, which, in turn, results in an increase in conflicting contact diameters (i.e. a flattening. area) of the ground engaging portion 132 with respect to the ground, and which, in turn, results in sliding of the wheel 10 on the ground and loss of momentum of the wheel 10. Since the hub 11 is substantially non-deformable during the push stroke of the wheel 10, the tire 13 will be deformed under pressure by the hub 11 and the ground especially during the push stroke, thereby resulting in flattening of the ground engaging portion 132 of the tire 13. Wedging the tire section primarily between portions 132 the shoulders 111 and a side of the tire deflection-controlling rim 112, leaving a relative small cross section of material that will allow for incremental deformation. Conventional solid tires are normally made from polyurethane, and are known to have a 10% deformation limit when exposed to pressure such that when the tire is deformed beyond this limit, the incremental stiffness of the same will increase sharply, this contrary to the incremental deformation which, in its turn, will grow very little and results in that the friction area will not grow in relation to the load and sliding of the conventional wheel 10 during the push stroke, especially on moist surfaces. The design for conventional tires normally seeks to compromise the deformation of the tire with rebound ability (or resilient property) of the tire. Rebound ability properties are coupled to how fast the difference between the actual and initial elasticity module (incremental tension force) returns deformations to another or the same shape that belonged to the initial elasticity module. Deformations that approach or exceed 10% of the actual cross section of the tire part under pressure load in the meantime tend to increase the incremental stiffness steeply, but hardly affect the incremental deformation and have hardly any effect on the rebound ability The loads that have hardly any effect on deformation are lost in damping and reduce the rebound ability or recycling of motion energy. The limited tire cross sections of existing tires designs that are wedged between a virtually stiff hub and the ground, allow only for relative small deformations and govern momentum loss via sliding friction, damping, and reduces by its stiffness vibration insulation and roadworthiness whereas more generous incremental deformation would aid rebound ability that would in its term governs the effective use of momentum stored in the tire and give vibration insulation (i.e. protecting a skater from the vibration the wheels generate at ground surface). As such, there is a need for a tire where prolonged incremental deformation keeps the incremental stiffness that low that rebound ability is not compromised. In other words, there is a need for a tire that stops to deform under pressure before the said 10% deformation level is reached, thus staying resilient and at the same time keeps ground contact at a limited number of conflicting contact diameters (i.e. keep the flattening area true to diameter). Invention wise this is solved by deforming the tire under tension as well as pressure and by attaching the tire to a secondary system that will start its rebound ability deforming well before the tire reaches its critical 10% deformation level under pressure. To deform a tire under tension is advantageous as the incremental stiffness that affects the deformability, grows much slower than under deformation by pressure.
Therefore, the object of the present invention is to provide a wheel for an in-line skate that is capable of overcoming the aforesaid drawbacks of the prior art.
According to the present invention, a wheel for an in-line skate comprises: a ring-shaped hub having a ring-shaped radially extending central stem that has two opposite axial sides and radial inner and outer ends, two symmetrical ring-shaped upper wings that extend oppositely and sidewisely from the radial outer end, and two symmetrical ring-shaped lower wings that extend oppositely and sidewisely from the radial inner end, each of the upper wings having an annular free end and an annular outer surface which extends sidewisely from the central stem to the free end; and a ring-shaped solid tire having a hub connecting ring portion that securely embraces the outer surfaces of the upper wings and that radially and outwardly extends relative to the outer surfaces of the upper wings. The tire further has a ground engaging ring portion that axially reduces and that radially and outwardly extends from the hub connecting ring portion, and that has a radial thickness greater than that of the hub connecting ring portion. The hub connecting ring portion cooperates with the upper wings to form an outer rim of the wheel that is capable of fulcruming about the central stem so as to permit bending of the ground engaging ring portion toward one of the opposite axial sides of the central stem when the wheel tips toward said one of the opposite axial sides of the central stem and pushes against the ground.